What Is the Upper Limb Abductor?
Muscles often work together to perform tasks. To move your upper limb, which describes the arm between the shoulder and elbow, several muscles work in concert. To abduct means to move away from the body; the upper limb abductors help you lift your arm upward at a 90-degree angle. The large deltoid muscle and the smaller supraspinatus muscle act as abductors.
DELTOID DEFINITION
You know where the deltoid muscle is situated if you've ever had an injection in your upper arm; the triangular deltoid is the muscle that your medical practitioner uses for injections. If you put your fingers on your upper arm and begin to raise your arm to a 90-degree angle, you can feel the deltoid muscle tighten. The wider part of the deltoid muscle attaches to the shoulder blade, or scapula, and the collarbone, or clavicle. The point, or apex, of the deltoid attaches to the humerus -- the upper arm bone -- about halfway down the bone.
SUPRASPINATUS DEFINITION
The supraspinatus muscle is smaller than the deltoid muscle. Situated at the top of the shoulder, this muscle forms part of the rotator cuff, a group of muscles that attach the humerus to the scapula. The arm and shoulder connection is a ball and socket joint; the rotator cuff helps keep the upper part of the humerus in place.
ACTIONS
The supraspinatus and deltoid muscles work together when you abduct your arm. The supraspinatus muscle initiates the action, because the deltoid muscle faces the wrong direction initially. The larger deltoid takes over the action, using the strongest part of the muscle -- the central section -- to lift the arm away from your body.
INJURIES
Rotator cuff injuries occur frequently, the result of wear and tear or from an acute injury. About 2 million people saw their doctor for a rotator cuff problem in 2008, according to the American Academy of Orthopaedic Surgeons. The supraspinatus muscle and tendon are the tissues most frequently injured in a rotator cuff injury. If you tear the muscle, raising your arm causes pain. If you have a severe tear, raising the arm becomes impossible.